GLOVE-BASED GESTURE RECOGNITION SYSTEM

GLOVE-BASED GESTURE RECOGNITION SYSTEM

CLAWAR 2012 – Proceedings of the Fifteenth International Conference on
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Climbing and Walking Robots and the Support Technologies for Mobile Machines,
Baltimore, MD, USA, 23 – 26 July 2012
GLOVE-BASED GESTURE RECOGNITION SYSTEM
MARIA EUGENIA CABRERA*, JUAN MANUEL BOGADO, LEONARDO FERMIN,
RAUL ACUÑA, DIMITAR RALEV
Mechatronics Research Group, Simon Bolivar University, ELE Bldg 3rd Floor, Lab 302.
Valle de Sartenejas
Caracas, Miranda 1080-A, Venezuela
Among the research topics developing within the Mechatronics Group at Simon Bolivar
University, there’s a field corresponding to Human-Computer Interaction (HCI), which is
the center of this paper, regarding the design and implementation of a hand gesture
recognition system, based on the information gathered with a data glove. The data glove
sensors convey the degree of flexion in each finger of the hand. Additionally, an
accelerometer sensor was placed on top of the glove to acquire the orientation of the hand
in three axes. With this information, the system would begin a decision making process
based on artificial intelligence tools, like neural networks, to recognize the American
Sign Language (ASL) signs for fingerspelling. The whole system is executed by
interfacing with a user, to collect the data and display the result of its classification.
1. Introduction
The use of gestures among humans, both in the form of pantomime or by using
sign language, is closely linked to speech and represents an effective way of
communication, used even prior to talking.
The formality of the set of rules chosen in each case is related to the validity
of the performed gestures, which means that a pantomime gesture could be
complimenting speech in a spontaneously and colloquial manner, or the same
gesture be considered a part of a sign language and posses a particular meaning,
whether it is to perform an action or convey some type of information (1).
There’s an approach within HCI, relating to the communication structures
between man and machines, and studying the physiological, psychophysical and
psychological aspects associated to the brain and its abilities to interpret
information. HCI generally focuses on the design, implementation and
evaluation of computer systems, through which a human operator performs
some kind of information exchange (2). Considering that the hands are used as a
means of communication, one could think of a system where their movement
could be interpreted as the input, to be analyzed and classified, using a
determined set of rules that would pass along the information.
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In order to decide which input device to acquire the user’s hand movements,
there are a few items to consider, regarding effectiveness, comfort of the user,
and the selection also needs to be suitable to the working environment to fulfill
the tasks set for the device within the system(3). In the topic of hand gestures
recognition, the input device must capture the position of each finger on the
hand, as well as the hand’s orientation in its rotation axis. The most commonly
used devices reported in the literature are data gloves for motion capture and
cameras for artificial vision. A more detailed revision of the state of the art will
appear in the following subsection.
The general idea of this particular project is based on the design of a system
that allows the recognition of a set of established gestures, such as the alphabet
in American Sign Language, performed by a user with a single hand, using a
data glove as an input device. In that system, artificial intelligence tools will be
used, like artificial neural networks, to achieve an interaction between a
computer and the user, where the first classifies and recognizes the gestures
executed by the latter. Within the alphabet of ASL, there are static and dynamic
gestures: static gestures can be accomplished by maintaining a pose of the hand,
while dynamic gestures join a specific pose of the hand with a movement.
1.1. State of the Art
Every research work starts by reviewing the literature on the subject, in order to
get a sense of what people are doing all around the world and to know the
possible applications and solutions presented for each topic specifically.
On the state of the art regarding the subject of gesture recognition, there are
many teams in many countries approaching the matter with two particular goals;
at least those two represent the most common among the reviewed literature.
One goal, seeks for gesture recognition to aid hearing impaired people, giving
them a way to interact with people who aren’t fluid in such language, through
the computer. The other goal relates to controlling robots, by the performed
gestures of its operator.
Another feature reviewed on the literature, was about the tools used to
achieve such said goals and the proposed solutions in each case. The work
published by Parton (4), reviews a number of approaches within the field of
Artificial Intelligence (AI) to effectively recognize and translate sign language:
from Artificial Neural Networks (ANN), Hidden Markov Models (HMM),
Artificial Vision, Virtual Reality, and motion capture using data gloves or
electromyographic (EMG) sensors. Which leads to believe that there are two
main approaches to recognizing hand gestures: one is based on motion capture
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of the user’s hand, while the other bases on artificial vision to determine the
gestures made in a specific time. Both approaches have their pros and cons.
Vision-based gesture recognition relies on image capture by one or more
cameras and applying algorithms to extract visual features, in order to recognize
the gesture made. The fact that the person making the gesture is totally detached
from the system is one of the most important benefits in working with visual
recognition. On the other hand, the system can be very susceptible to changes in
the environment, like lighting or background figures and colors that could affect
the process.
The work by Ricco & Tomasi (5), looks for recognizing features not only in
the images where there is a gesture but they also consider in their algorithm the
frames of transition to recognize gestures; while Gui et.al (6) focus on intrinsic
characteristics of the gestures to recognize them. Another method reported by
Malima et.al is to obtain the image centroid to recognize positions of the hand to
command a robot to move. (7)
The approach based on capturing the user’s motions, physically links the
user to the system but in return, it detaches it from the changes in the
environment giving the opportunity to use the system in different places and
obtaining the same results. The problem with incorporating the user to the
acquisition process is that it causes a discomfort on the user, since their hand is
no longer as free as it would be in a normal scenario. The most common device
used in the literature is the data glove, to acquire the flexion degree of each
finger in the hand. Another system (8) bases its input device on EMG sensors
placed on the forearm of an operator to control a robot with grasp recognition.
On most of the research work reviewed where a data glove was used the
problem to be solved was the translation of sign language to written or spoken.
As mentioned previously, most are based on a pre-established sign language to
recognize a subset of letters on the alphabet in each case, commonly the static
gesture letters. The work of Parvini et.al compares the result of three
configurations for ANN classifying the static gestures of ASL acquired by a
dataglove, one with neural networks alone, one with multi-layer networks
working with template matching, and finally a gesture recognition system using
bio-mechanical characteristics. The best results were obtained from the first and
last configuration (9). In other papers, the system architecture is a bit more
elaborate, like the case of Fels & Hinton, where they use two data gloves and a
voice synthesizer with intonation control using a pedal. (10)
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2. Architecture System Description
The proposed system for recognizing hand gestures begins and ends with the
user. In between there are five stages: input, acquisition, preprocessing,
classification and results presentation.
Figure 1. Diagram for the System Architecture.
As presented in Figure 1, the user places the input devices on his right hand;
the input devices consist on the 5DT Data Glove 5 Ultra to gather information of
the flexion degree of each finger of the hand and a 3-axis accelerometer place on
the back of the hand to know its orientation. The data from the accelerometer
goes through the acquisition stage, where an ADC converts the values of each
axis to 14-bit numbers and passes them along to the computer for the
preprocessing stage. In that stage, the information of the data glove, that
communicates directly to the computer and the acquired data of the
accelerometer go through a calibration and standardization process and then it is
stored to use it as inputs in the classifying stage. Said stage is about using an
artificial intelligence tool, such as artificial neural networks, to recognize
gestures based on the experience of the previously collected data. With a trained
network, an interface is developed to present the results of the gesture
classification back to the users.
The proposed system innovates comparing to previous works by adding the
accelerometer to gather information of wrist rotation, which allows identifying
some ASL gestures for letters such as H and U that hold an identical position for
all fingers in the hand and differ on the wrist rotation, another examples are K
and P, also G and Q. Previous works, such as (9), select only one of the similar
letters to input the system and be recognized by it. On figure 2, the similarities
between the previously named letters are shown.
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Figure 2. Similarities between ASL gestures for specific letters.
The final interface is made in National Instruments Labview® Software, as
shown on Figure 3; the software is also used to gather the sensors information
and store the data to be used in Matlab® for the ANN configuration and
training.
Figure 3. Interface in Labview® to present the final results of the Hand Gesture Recognition System
3. Classification Results
The Artificial Intelligence tool selected for this particular project was multilayer
perceptron feed-forward neural networks with backpropagation as a training
algorithm.
Several ANN were tried in order to obtain the best results in correctly
classifying the data acquired and stored from the input devices. The total data
used as input is 5 for each flexion sensor on the hand’s fingers and 3 for each
axis of the accelerometer. So the input layer of the system’s network is set to 8.
About the output layer, there are as many neurons as letters to classify and an
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extra one for gestures that aren’t letters, such as transition gestures or gestures
not included in the ASL alphabet; the letters to be included in the process are the
ones based on static gesture, excluding J and Z. Which leaves the output layer
set to 25 neurons. Each input cluster will be feed-forwarded through the hidden
layer and the output layer to activate one of the neurons in the output layer. The
values of the output layer may vary from 0 to 1 with a sigmoid function.
The number of neurons in the hidden layer (H.L) was the parameter
changed throughout the selection of the best performing network. The other
parameters were kept the same in each test: 5300 training patterns, with an
average of 200 per letter and 500 for transition gestures. A set of 1200 patterns
were left apart for validation purposes. Each training process was made with a
learning rate of 0.015, a maximum of 100 iterations and a mean squared error
target of 1.10-5. The results are shown on Table 1.
Table 1. Training Results and Validation Percentages for different ANN
configurations, changing the number of neurons in Hidden Layer.
H.L
Neurons
Training
MSE
Training
Iterations
Training
Time
Val. Classification
%
40
5,25.10-3
61
18'16''
92,02
50
60
4,16.10-3
4,10.10-3
83
62
33'36''
34'23''
92,7
94,07
70
3,71.10-3
64
47'21''
93,39
4. Conclusions
The performance of the Glove-Based Gesture Recognition System is directly
related to the effectiveness of the classification stage within it. Based on the results
given by different number of hidden layers in the neural network, the best
validation percentage obtained was when there were 60 neurons in the hidden
layer. Among the many benefits of using neural networks for classification duties,
there is the ability to adapt and generalize when properly trained, and they can be
easily retrained to adapt its synaptic weights to variations in the system.
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